South Korea, Japan, and the US are taking the
next step after the sinking of the Cheonan and bringing the issue before the UN Security Council. The Security Council is the only body of the UN with any teeth (ie the ability to use force or issue sanctions), but it has 5 vetoing members. Two of these members do not want much more an a strongly worded letter of censure.
The US is at least paying lip service to the idea of tougher enforcement of the sanctions against North Korea that is already in the books. It will be interesting to see where this leaves as actual enforcement of the sanctions might require the boarding of DPRK ships.
I think the identification and tracking of North Korean trading entities, many of which obfuscate their country of origin, should be a high intelligence priority for the US. After that it may be possible to create heaps of trouble for them in which ever country they are operating in by exposing illegal activity and doing what Americans do best... suing the crap out of them.